1. Field of the Invention
The present invention relates to a construction of an ink-jet head for squirting ink droplets at a print surface to form an image thereon.
2. Description of the Related Art
Ink-jet recording equipment, such as an ink-jet printer, is equipped with an ink-jet head. In general, the ink-jet head comprises a plurality of nozzles to squirting ink at a print surface, a plurality of pressure chambers arranged in correspondence to the nozzles, and a common ink chamber to distribute the ink and feed it to the plurality of pressure chambers. Some ink-jet heads are structured so that the pressure chambers and the common ink chamber are formed in an interior of the ink-jet head, for the purpose of downsizing the ink-jet head.
In the known ink-jet heads, the common ink chamber is connected to an ink supply source such as an ink cartridge through an ink feed port opening in an outer surface of the ink-jet head.
In the construction of the ink-jet heads mentioned above, the ink fed from the ink supply source to the common ink chamber is distributed and supplied to the respective pressure chambers. Each pressure chamber is provided with an actuator comprising e.g. a piezoelectric element, so that the ink is energized by the drive of the actuator and is squirted from the nozzles to a print surface to form a desired image thereon.
In general, the method of laminating a multiple of thin flat plates, each having the pressure chambers and the common chamber previously formed by etching is widely adopted to form an ink passage including the pressure chambers and the common ink chamber in the interior of the ink-jet head.
Some of the known ink-jet heads have a restricted passage to restrict the pressure orienting toward the common chamber so that the pressure exerted on the ink in the pressure chamber by the drive of the actuator can be effectively oriented toward the nozzles to increase a speed of the ink squirting from the nozzles. The restricted passage is formed in such a way that its cross-sectional area is made smaller than a cross-sectional area of the pressure chamber to provide a passage resistance against a back-flow of the ink from the pressure chambers to the common ink chamber.
In the conventional ink-jet head, the restricted passage is additionally formed by half etching or equivalent in the flat plate in which the pressure chambers are previously formed. Also, the restricted passage is extended in a longitudinal direction of the pressure chamber. This construction requires that the flat plate should have at least a width corresponding to a length of the pressure chamber plus a length of the restricted passage, for forming the pressure chambers and the restricted passage in the flat plate. This makes it hard to meet the demands for realization of a compact ink-jet head with a high-integration and high-density passage arrangement accompanied by the needs of a high resolution of a picture.
Also, the pressure chambers and the restricted passage are both the parts for which high dimensional precision is required in the ink-jet head. Forming the both in the same flat plate means that a complicated configuration for which high dimensional precision is strictly required is formed in a flat plate and thus accompanies difficulties in production. This contributes to reduction in yield and increase in production cost.
Further, when the restricted passage is formed in a grooved shape in the flat plate by using the half etching technique, the half etching depth must be controlled with strict precision to produce a required passage resistance with high precision. This also contributes to reduction in yield and increase in production cost.
Some known ink-jet heads are constructed so that the restricted passage is formed to let the ink to flow in the thickness direction of the flat plate. With this construction, as a result of the length of the restricted passage being limited to the plate thickness at the maximum, the restricted passage is shortened too much for the restricted passage to provide sufficient resistance against the back-flow of the ink trying to flow back to the common ink chamber from the pressure chamber side. This produces the problem of decrease in a speed of the ink squirting from the nozzles.
Further, the ink-jet head of the flat-plate laminated structure makes it easy to form some stepped portions in the ink passage formed in an interior of the ink-jet head, so that stagnation of the ink is apt to occur at those stepped portions and bubbles are apt to grow thereat. This prevents a smooth ink flow and eventually causes the trouble that the ink squirting failure (missing dot) is often produced. Although the technique of using a purge mechanism, built in the ink-jet recording device, to forcibly suck the ink bubbles from the nozzles is also known, since it is hard to purge the bubbles from the locations where the stagnation of the ink occurs, even the purge mechanism often has difficulties in purging the bubbles.